This invention relates to a key telephone set and a key telephone system including the key telephone set, in particular, to a key telephone set having interchangeable function units which can be attached/detached to/from a telephone main body without disassembly of the telephone main body.
The key telephone system generally comprises a main device (or a key service unit) and a plurality of key telephone sets connected to the main device.
To meet various demands from users, it is necessary to provide some or many types of telephone sets. For instance, a user needs a display portion while another user needs no display portion. Furthermore, a user needs a small number of line selection buttons for extensions and outside lines while another user needs a large number of the line selection buttons.
An existing key telephone set comprises a telephone main body, a display assembly and a selection button assembly. The display assembly and the selection button assembly are attached to the telephone main body. The display assembly and the selection button assembly can be detached from the telephone main body when the telephone main body is disassembled. Providing interchangeable display assemblies and interchangeable selection button assemblies correspond to providing various types of telephone sets. That is, functions of the key telephone set can be easily changed by the use of different display and different selection button assemblies together with the telephone main body. Such a key telephone set is disclosed in Japanese Unexamined Utility Model Publication No. 5-6961.
Another existing key telephone set comprises a telephone main body, dial and function button units and a decorative panel for positioning the button units on the telephone body. The decorative panel can be detached from the telephone main body from the top surface side of the telephone main body. The dial and function button units can be freely separated from the telephone main body when the decorative panel is detached from the telephone main body. This is because the dial and function button units are merely placed on a predetermined position of the telephone main body. Accordingly, specification of the key telephone set is easily changed by changing the button units for different button units. Such a key telephone set is disclosed in Japanese Unexamined Patent Publication No. 2002-75114.
As a related technique, there is a radio communication apparatus, which is not a key telephone set. The radio communication apparatus comprises a main body and a detachable operation button block which is attached to the main body and which can be detached from the main body. Functions of the radio communication apparatus are changed by the changing the operation button block for a different operation button block Such a radio communication apparatus is disclosed in Japanese Registered Utility Model Publication No. 3004142.
However, the existing key telephone set using the display and the selection button assemblies has a fault that the telephone main body must be disassembled to detach the display and the selection button assemblies from the telephone main body. This is because each assembly has hooks and claws for engaging with the telephone main body while the hooks and the claws can not be disengaged from one another from the outside of the telephone main body.
Furthermore, the other existing key telephone set using the button units and the decorative panel has a fault that it is impossible to meet the user's demands about the number of the line selection buttons and/or about having a display unit or not. The related radio communication apparatus has as similar fault because the operation button block is collectively attached/detached to/from the main body.